In general, a fuel cell system that is mounted in a fuel cell vehicle is configured to supply hydrogen, which is used as fuel, and air to a fuel cell stack, and electricity is produced by an electrochemical reaction of the hydrogen and the oxygen within the fuel cell stack. The fuel cell vehicle is driven by operating an electric motor with electricity produced by the fuel cell stack. The fuel cell vehicle further includes a high voltage battery to use energy of the fuel cell system and energy of the high voltage battery.
As shown in FIG. 1, the fuel cell vehicle including the fuel cell system and the high voltage battery typically includes a bidirectional converter 20 that effectively controls energy flow from both the fuel cell system and the high voltage battery. The bidirectional converter may be a bidirectional direct current-direct current (DC/DC) converter or a large-capacity bidirectional DC/DC converter. In addition, the fuel cell vehicle includes a fuel cell controller 10 configured to operate the fuel cell vehicle, as shown in FIG. 1. The fuel cell controller may be referred to as a fuel-cell control unit (FCU). In FIG. 1, reference numeral 30 indicates a fuel cell system, 40 indicates an inverter, 50 indicates a high voltage battery, 60 indicates a motor, 70 indicates a low voltage DC/DC converter, and 80 indicates an auxiliary battery. The indicated elements are well-known to those skilled in the art, and thus detailed descriptions thereof will be omitted.
Referring to FIG. 1, an energy flow, an energy amount, and a mode switch associated with charging and discharging of the high voltage battery 50 may be determined based on commands from the fuel cell controller 10. A discharging energy supplied from the high voltage battery 50 is supplied to electrical loads of a fuel cell vehicle via the bidirectional converter 20 in which power conversion is performed. When a state of charge (SOC) of the high voltage battery 50 decreases while the fuel cell vehicle is being driven, the bidirectional converter 20 supplies energy from the fuel cell stack to the high voltage battery 50. When a braking signal in the fuel cell vehicle occurs, the bidirectional converter 20 supplies regenerative braking energy produced by regenerative braking based on a command of the fuel cell controller 10 to the high voltage battery 50 to charge the high voltage battery 50.
The above-described energy flow may be processed within several hundred milliseconds to several seconds while the fuel cell vehicle is driving. However, since the bidirectional converter performs a predetermined control based on commands from the fuel cell controller that is a superordinate controller over the bidirectional converter even in a transient state in which a rapid energy conversion is required in the fuel cell vehicle, an overshoot/undershoot voltage may abruptly occur. The overshoot/undershoot voltage influences an output voltage of the high voltage battery, causing abrupt shaking, breakdown by overvoltage, and durability reduction of components while the fuel cell vehicle is being driven.
The above information disclosed in this section is merely for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.